The production of white oils by hydrogenation of different types of raw materials coming from oil is well known and is used normally commercially.
U.S. Pat. No. 3,328,293 describes a process . for the production of white oils from the distillation of mineral oil which contains aromatic compounds naphthalenes and paraffins. The process consists of catalytic hydrogenation, using a sulfur resistant catalyst, which converts the strongly polar compounds into apolar ones, increasing the naphthalene and paraffin content of said distillate. Subsequently, this distillate is subjected to fractionation, in a silica gel or aluminum oxide absorption column to separate a paraffin hydrocarbon fraction and another naphthalene hydrocarbon fraction useable as white oil.
The use of an alkylate fraction which contains sulfur, with a boiling point above the range of gasoline, with a useful feed for a process of obtainment of white oil is referred to in U.S. Pat. No. 3,392,112. Bascially, this is a two step process for the elimination of sulfur and aromatic compounds, in which the first step consists of catalytic hydrogenation with a sulfur resistant catalyst, which yields a partially hydrogenated product with a low sulfur content so that it does not adversely affect the nickel catalyst and diatomaceous catalyst of the second step. This second hydrogenation is carried out at a pressure less than 2,500 psi and other suitable conditions to give a useful product such as white oil.
Among other patents which partially or totally describe the raw material of the present invention, U.S. Pat. 4,240,900 and Spanish patent No. 548,767 are included.
The hydrogenation processes for the production of white oils which use as a catalyst a metal from the iron group on an inorganic oxide refractory support are also known in literature. For example, Spanish patent No. 548,767 describes the use of a hydrogenation catalyst which comprises a metal of Group VIII especially platinum or nickel, upon a porous inorganic support for the production of white oils. However, this Spanish patent claims the use of a catalyst which contains only 5% to 20 % by weight of the metallic component. U.S. Pat. No. 3,658,692 describes a process for the production of white oil by hydrogenation of a white oil base, with a low sulfur content, in the presence of a catalyst which contains nickel, cobalt and/or iron, with an alumina, silica-alumina or boron base and where the catalyst is prepared in a specific manner. A hydrogenation catalyst which contains from 25% to 75% by weight of a metallic component of Group VIII, is described in U.S. Pat. No. 4,318,829. The described hydrogenation catalyst also includes aluminum and one or more metallic components of Group IIa, upon porous particles, with a catalyst characterized by having a BET surface area of 150-350 m.sup.2/ g.
Likewise, the use of a two step hydrogenation process for the production of white oils is well known. However, the described two step processes, either refer to the use of two reaction areas, the first one of hydrotreatment and then a second one of hydrogenation, as in U.S. Pat. No. 3,431,198, or else they describe a process which comprises two successive hydrogenation steps, such as U.S. Pat. No. 3,392,112 cited above.
There are many other patents which describe similar processes of catalytic hydrogenation of heavy hydrocarbons for the obtainment of white oils, but the process object of the present invention differs from the ones presently existing, in that the first step of the same is strictly a pretreatment step of the feed, which does not consist of any catalytic hydrogenation process, but rather a treatment of absorption with selective elimination of the heaviest components, while the second step is a more or less conventional type hydrogenation.
Consequently, it is an object of the present invention to provide an improved process for the obtainment of white oils from heavy alkylates.
Another object of the present invention is the furnishing of a process for the obtainment of white oils from heavy alkylates, in which a first step or selective pretreatment is used, consisting of percolation of the heavy alkylate through a bed of activated magnesium silicate, which furnishes important advantages in comparison with the normal methods and use, a first step of a substantially different nature and generally a more complicated and more costly process of catalytic hydrogenation.
Other objects and advantages of the invention will be inferred from the following description.